Image reading apparatus with a half mirror

ABSTRACT

An image reading apparatus high in illumination efficiency which can illuminate an image reading position by use of at least one polarizing element is disclosed. The image reading apparatus can illuminate an object to be image read sufficiently, even if the object is floated away from a predetermined image reading position. In the image reading apparatus, the major illumination light L2 from an illumination unit 1 and the light L2 reflected from the object and then introduced onto light-electricity transducing elements are located on substantially the same plane, and further the polarizing elements 2 and 3 are interposed between the illumination unit 1 and the object 20 and between the object 20 and the light-electricity transducing elements 7, respectively.

TECHNICAL FIELD

The present invention relates to an image reading apparatus used for animage scanner, digital copying machine, facsimile, etc. to read imagesinto a computer, mainly.

BACKGROUND ART

The image reading apparatus is generally composed of an illuminationunit, an image forming system such as a lens, and light-electricitytransducing elements. The composing elements required for reading animage are substantially the same in the image scanner, the digitalcopying machine, and the facsimile, therefore these composing elementsare described by taking the case of an image scanner, by way of example.

In the ordinary image reading apparatus, a linear light source such as amercury fluorescent lamp or halogen lamp is used as the illuminationunit; a lens of about (7 against 1) reduction ratio is used as the imageforming system; and linearly arranged CCDs are used as thelight-electricity transducing elements. An example of the prior artimage reading apparatus is disclosed in Japanese Published UnexaminedPatent Application No. 60-148269. FIG. 9 is a cross-sectional viewshowing this prior art image reading apparatus, in which the lightreflected from an image 20 illuminated by an illumination unit 22 isimage formed on the CCDs 25 of the light-electricity transducingelements through a mirror 23 and a lens 24 which constitute an imageforming system. In the image forming system as described above, in orderto increase the image reading speed, the following four methods havebeen so far adopted: (1) the sensitivity of the light-electricitytransducing elements 25 has been increased; (2) a bright lens has beenused by increasing the aperture ratio (F-number) of the image formingsystem 24; (3) the quantity of light from the illumination unit 22 hasbeen increased; and (4) the quantity of light applied onto thelight-electricity transducing elements 25 has been decreased to increasethe reading speed, with decreasing the S/N ratio; that is, withdeteriorating the image quality. Conventionally, the reading speed hasbeen so far improved mainly by increasing the quantity of light emittedfrom the illumination unit 22 as described in item (3) above.

However, when the image reading speed is required to be further improvedto such an extent that 20 pieces of A4-sized paper image can be read perminute, for instance such as in the case of an analog copying machine,if the quantity of light from the illumination unit is simply increased,the size of the image reading apparatus is inevitably increased. This isbecause a heat radiation plate or an exhaust heat fan are additionallyrequired to exhaust heat generated by the illumination unit and furtheran additional air flow path will be necessary to exhaust the heat.

In the prior art optical system, the utilization efficiency of lightemitted from the illumination unit is very low. Here, "illuminationefficiency" can be defined by taking a ratio of the quantity of lightfor illuminating an object to be image read to the quantity of light forilluminating an area on the object to actually read the image. FIG. 10shows a distribution of the quantity of light for illuminating theobject 20 to be image read. As shown in FIG. 10, the ordinaryillumination unit of the image reading apparatus illuminates a width ofabout 10 to 30 mm in the secondary scanning direction on the object 20to be image read. Here, when taking into account the case where thereading width is 300 dpi, the light is applied upon a width of 30 mm atthe maximum in order to read an image of an object 20 in about 85 μmwidth. That is, the illumination efficiency is 0.85% to 0.28% inaccordance with the following equation: ##EQU1##

In other words, the light of 99.15 to 99.72% is not only wasted but alsoneedlessly illuminates the area other than is necessary to read theimage, thus causing the generation of stray light. As a result, therearises a problem in that the quality of gradient in the read image isdeteriorated markedly.

The reason why the illumination width as wide as 10 to 30 mm is securedin the prior art image reading apparatus is to keep the quantity ofilluminating light at a constant level at the image reading positioneven if the object 20 is somewhat floated upward from the base position.FIG. 11 is an illustration for assistance in explaining theabove-mentioned reason, which is an enlarged view showing the imagereading position shown in FIG. 9. The central ray of light La forilluminating an object 20 is allowed to be incident upon the object 20at an angle of 45 degrees, for instance. Here, assuming that the object20 is floated up by a distance Δh from a glass base 21, the position P1at which the central ray of light La emitted from the illumination unit22 illuminates the object 20 is shifted to the position P2. In thiscase, however, since the optical image reading system is located on theoptical axis Lb, the position at which the object 20 to be image read isstill kept at the position P1'. In other words, there exists an offsetΔy between the central position P2 of the illumination light and theimage reading position P1'.

Consequently, in order to read the object 20 floated upward away by 20mm from the glass base 21, for instance, it is necessary to secure thewidth of the illumination light to such an extent as to correspond tothe above-mentioned distance of the object 20 from the glass base 21 inthe secondary scanning direction (in a term of the image readingapparatus) or in the arrow direction (shown at the center of FIG. 11).The illumination efficiency is deteriorated by the reason as describedabove.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide an image readingapparatus of high illumination efficiency, which can illuminateefficiently a position at which an object to be image read is located.The other object of the present invention is to provide an image readingapparatus low in the light output of the illumination unit, high inimage reading speed, and compact in construction.

The present invention provides an image reading apparatus comprising:illuminating means for illuminating an object to be image read withlinearly polarized light; shutting means for shutting off regularreflection light component included in the light reflected from theobject on a plane substantially the same as the linearly polarized lightfor illuminating the object; and light-electricity transducing means fortransducing the reflection light component other than the regularreflection light component into electric signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an essential portion of a firstembodiment of the image reading apparatus according to the presentinvention;

FIG. 2 is an illustration showing an essential portion of a secondembodiment of the image reading apparatus according to the presentinvention;

FIG. 3 is a front view showing a partial reflection mirror used for theimage reading apparatus shown in FIG. 2;

FIG. 4 is a perspective view showing an illumination unit used for theimage reading apparatus shown in FIG. 2;

FIG. 5 is a cross-sectional view showing the image reading apparatus,taken along the line B--B' in FIG. 4;

FIG. 6 is a cross-sectional view showing an optical reading system usedfor a third embodiment of the image reading apparatus according to thepresent invention;

FIG. 7 is a cross-sectional view showing an optical reading system of afourth embodiment of the image reading apparatus according to thepresent invention;

FIG. 8 is a cross-sectional view showing an optical reading system of afifth embodiment of the image reading apparatus according to the presentinvention;

FIG. 9 is an illustration showing a prior art image reading apparatus;

FIG. 10 is a graphical representation showing a distribution of thequantity of light for illuminating an object to be image read in theprior art image reading apparatus; and

FIG. 11 is an enlarged view showing the image reading position in theprior art image reading apparatus shown in FIG. 9.

BEST MODES FOR EMBODYING THE INVENTION

A first embodiment of the image reading apparatus according to thepresent invention will be described hereinbelow with reference to theattached drawings.

As shown in FIG. 1, an illumination unit 1 is a linear light source suchas a halogen lamp. The light L1 emitted by the illumination unit 1 istransformed on an X-Y-Z coordinate system into polarized light L2 of theX-axis direction (a vertical direction on the paper) through a polarizer2 (first polarizing element). After having been reflected by a halfmirror 4, the light L2 illuminates an object 20 to be image read. Thelight L3 reflected by the object 20 is passed through the half mirror 4,reflected by a mirror 5, and then passed through an analyzer 3 (secondpolarizing element). The polarization direction of this analyzer 3 isthe Z-axis direction. The light L4 passed through the analyzer 3 isimage formed on light-electricity transducing elements 7 through animage forming system 6 composed of a group of lens. The image formingsystem 6 is so arranged that an image of the object 20 can be imageformed on the light-electricity transducing elements 7 at a reductionratio of 7 against 1, for instance.

In the image reading apparatus shown in FIG. 1, the X-axis is referredto as the primary scanning direction, and the Y-axis is referred to asthe secondary scanning direction.

Here, the functions of two polarizing elements of the polarizer 2 andthe analyzer 3 will be described. In designing a prior art image scanneras an example of the conventional image reading apparatus, the opticalpath of the light emitted by the illumination unit for illuminating anobject is usually arranged at an angle of about 45 degrees with respectto the optical path of the light reflected from the object and then ledonto the light-electricity transducing elements 7. This is because whena lustrous object such as a photograph is image read, the read image isdeteriorated by the light of regular reflection component. The light ofthe regular reflection component not only deteriorates the precision ofphotographic density markedly, but also results in an image which is outof focus.

In contrast, in the embodiment of the present invention, theillumination light L2 and the reflected light L3 are both locatedsubstantially on the same plane. Therefore, the light L3 reflected fromthe object 20 shown in FIG. 1 is mixed with the light of regularreflection component. However, the regular reflection component light isthe polarized light of the same direction (X-axis direction) as thepolarizer 2, so that the regular reflection component light is almostshut off by the analyzer 3 arranged in the direction (Z-axis direction)perpendicular to the polarization direction (X-axis direction) of thepolarizer 2. On the other hand, the light reflected from the object 20other than the regular reflection light component, that is, thediffusion reflection light includes polarization components of variousdirections determined according to the shape of the object 20.Therefore, the light reflected from the object 20 can be passed throughthe analyzer 3. On the basis of the above-mentioned function attained bythe polarizer 2 and the analyzer 3 in combination, it is possible toeliminate the light of the regular reflection component reflected fromthe object 20, in order to prevent the image quality from beingdeteriorated.

The reading operation will be described hereinbelow. The above-mentionedoptical system is mounted on a carriage 10, and illuminates a part ofrows S (extending in the X-axis direction or the primary scanningdirection) on an image-read object 20 placed on a glass base 21.Further, the reflected light is image formed on the light-electricitytransducing elements 7. The light-electricity transducing elements 7 areof a linear image sensor such as CCDs. Therefore, it is possible to readimage data corresponding to one column portion of the partial row S onthe object 20 through an electronic circuit (not shown). Thereafter, thecarriage 10 is moved in the Y-axis direction in FIG. 1 by a distancecorresponding to the resolving power by driving means 30 through atiming belt 32. By repeating the above-mentioned operation, it ispossible to read the image all over the object 20 to be image read.

In the above-mentioned image reading apparatus, since the illuminationlight L2 and the light L3 reflected from the object 20 are located on aplane including the Y-axis and the Z-axis perpendicular to the X-axis asthe primary scanning direction to the surface of the object 20 even whenthe object 20 floats away upwardly; possible to illuminate the sameposition of the object 20. Accordingly, it is possible to prevent thequantity of illuminating light from being reduced due to the floating-upof the object 20, being different from the case of the prior art imagereading apparatus. In addition, since only an illumination widthaccording to the width to be image read is determined, it is possible toreduce the quantity of illumination light markedly, as compared withthat of the prior art illumination unit.

Here, the required quantity of illumination light will be comparedbetween the prior art apparatus and the apparatus of the presentinvention. In the prior art image reading apparatus, if the intensity ofillumination light on an object 20 is 2000 lux, and the illuminated areais 22 cm long and 3 cm wide, the required quantity of luminous flux is13.2 lumen. On the other hand, in the case of the present embodiment, ifthe intensity of illumination light is 2000 lux, and the illuminatedarea is 22 cm long and 0.0085 cm (=300 dpi) wide, the required quantityof luminous flux is 37.4 millilumen. In the case of the presentembodiment, since the light transmissivity of the polarizer 2 and theanalyzer 3 is approximately 10%, an extra quantity of light is requiredfor the illumination unit 1 under consideration of the quantity of lightto be cut-off through these polarizing elements. When 10 times quantityis assumed to be required, the required quantity of luminous flux isabout 0.4 lumen, in practice.

As understood by the above-mentioned comparison, in the image readingapparatus according to the present invention, there exists an advantagein that the required quantity of illumination light is aboutone-thirtieth (1/30) at the maximum of that of the prior artillumination light.

The above-mentioned advantage results in the fact that the power of theillumination unit can be reduced; the size of the image readingapparatus can be reduced; and simultaneously the image reading speed canbe increased 30 times, in the case where the illumination unit having anoptical output the same as that of the prior art illumination unit isused.

Additionally, in the image reading apparatus according to the presentinvention, since the illumination light L2 and the reflected light L3are both located on the same plane, it is possible to provide an imagereading apparatus which can read, without producing any shade portions,images of three-dimensional objects, for instance such as fruit ascherries, two sheet of photographs stuck together with paste andtherefore having a stepped portion, books or magazines opened andtherefore having sloped surface portions, etc.

Further, when the a diaphragm 61 whose diameter is adjustable isprovided for the image forming system 6 to increase the aperture ratio(F-number)of the image forming system, it is possible to broaden thefocusing range in the direction that the object 20 is floated away fromthe surface of the glass base 21. In this case, for example, thevariable diaphragm 61 is so constructed as to be adjustable in responseto a control signal applied to a diaphragm driving system 62 from a hostcomputer (not shown). Further, the user selects any given allowablefloating distance of an object upward away from the glass base,according to the necessity, so that the image can be located in focuswithin the range between 30 to 3000 mm in the Z-axis direction away fromthe glass base 21. As a result, it is possible to read an image ofthree-dimensional object 20 such as a wrist watch, a gem, a stuffeddoll, etc. in addition to a sheet-like object, without producing anyout-of-focus images.

FIG. 2 shows a second embodiment of the image reading apparatusaccording to the present invention, in which a linear polarizing element2 is interposed between a partial reflection mirror 251 and anillumination unit 211. Further, FIG. 3 shows the partial reflectionmirror 251. This partial reflection mirror 251 is formed byvacuum-depositing aluminum thereonto, except the middle portionextending along the longitudinal direction thereof. Further, a linearpolarizing element 3 having a polarization component in the Z-axisdirection is interposed between the image forming system 6 and the CCDs7 of the light-electricity transducing elements.

The light L21 transmitted by an illumination unit 211 is transformedinto the linear polarized light of the X-axis direction through a linearpolarizing element 2, passed through a slit 254 formed in the partialreflection mirror 251, and then applied substantially perpendicularlyupon a reading position S of an object 20. A regular reflectioncomponent light mixed with the light L22 reflected from the object 20 isreflected by an outer perimeter portion 255 of the partial reflectionmirror 251, further reflected by two mirrors 252 and 253, and thenpassed through the image forming system 6. In this case, however, sincethe direction of linear polarization of the regular reflection light isin the X-axis direction, the regular reflection light cannot passthrough the polarizing element 3 of Z-axis direction.

On the other hand, a diffusion light component also reflected by theobject 20 is reflected by the outer perimeter portion of the partialreflection mirror 251, reflected by the mirrors 252 and 253, and thenpassed through the image forming system 6. Further, at least some of thediffusion light is in the Z-axis direction can pass through the linearpolarizing element 3. As a result, reflection light L22 of the object 20is image formed on the CCDs 7, so that the image can be read.

In this embodiment, the illumination light L21 emitted from theillumination unit 211 is very high in directivity, so that theillumination light can illuminates the reading position S of the object20 mounted on the glass base 21 effectively from a position 50 mm ormore far away from the object 20.

The reason why the luminous flux of high directivity is emitted from theillumination unit 211 is as follows: FIG. 4 is a perspective viewshowing the illumination unit 211, and FIG. 5 is a cross-sectional viewtaken along the line B--B' shown in FIG. 4. The illumination unit 211 ismanufactured by forming an air-tightly closed glass vessel as shown inFIG. 4, evacuating the glass vessel down to such an extent of 10⁻³ to10⁻⁵ Pascal in degree of vacuum through an evacuation tube 212 made ofglass, and by heating the glass with gas combustion to melt the tube andto seal the vessel. The light converging member 213 is formed of glassand into cylindrical shape. At a part of the inside of the illuminationunit 211, a fluorescent substance 215 for cathode luminescence from 0.1to 100 mg/cm² and most preferably 4 mg/cm² is applied in strip fashionalong the longitudinal direction thereof, and further the appliedfluorescent substance 215 is covered by an anode 214 having a thicknessform 0.1 to 0.4 μm and formed by vacuum-depositing aluminum as shown inFIG. 5. A practical example of the fluorescent substance is ZnS:Cu, Al.

Further, as shown in FIG. 4, a cathode wire 216 is provided so as toextend along and over an inner backboard plate 217. The cathode wire 216is a fine wire made of tungsten and having a diameter of 5 to 100 μm,which is covered with an electron emitting substance such as bariumoxide (not shown), for instance to increase the thermoelectron emittingefficiency. Further, a grid 218 is arranged between the anode 214 andthe cathode 216. The grid 218 is a net-like thin metallic plate made ofstainless steel, nickel, aluminum, etc. and formed with holesmanufactured by punching-out or electrocasting. Further, a U-shapedbackboard electrode 232 is interposed between the cathode wire 216 andthe backboard plate 217.

The above-mentioned cathode wire 216 and the backboard electrode 232 areconnected electrically to external terminals provided away from theillumination unit 211 through leads 219 shown in FIG. 4.

The operation of light emission will be described herein below. Whencurrent is passed through the cathode wire 216 by a power source (notshown), thermoelectrons 226 are generated from the surface of thecathode wire 216 due to the Joule heat. The generated thermoelectronsare accelerated toward the anode 214 to which a high tension of about 8kV is applied. The thermoelectrons emitted against the anode 214 passthrough the anode 214 of thin film aluminum, and excite the fluorescentsubstance 215 to emit visible radiation L5 to the outside of theillumination unit 211 on the basis of the principle of cathodeluminescence light emission.

The light converging member 213 will be described hereinbelow. Asalready described, this light converging member 213 is of a glasscylinder to which a fluorescent substance 215 is applied in stripefashion. The width of the stripe is from 0.1 to 10 mm, which is adjustedaccording to the quantity of the emitted light. The current density ofthe emissive thermoelectrons 226 is determined by the brightnesssaturation of the fluorescent substance, and therefore about 200 μA/cm²at the maximum. The visible radiation L5 generated from the lower endportion P5 of the light converging member 213 are emitted as a planarlight ray of high directivity by the function of the optogeometricallens of the light converging member 213.

To obtain the illumination unit of a high directivity, it is possible toadopt other methods of using an LED array and emitting light through alight converging member similar to that of the second embodiment.

FIG. 6 shows a third embodiment of the present invention, in which apolarized beam splitter 301 and a quarter wavelength element 302 areinterposed between the partial reflection mirror 251 and the object 20.

The behavior of the light along the optical path will be described. Thelight L31 emitted by the illumination unit 1 is transformed into alinearly polarized light of Z-axis direction (shown in FIG. 6) through alinearly polarizing element 331, and then reflected by a partialreflection mirror 251 toward an object 20 along an optical path roughlyperpendicular to the object 20. Here, a polarized beam splitter 301 isprovided with the function of passing light other than the linearpolarized light of X-axis direction, so that the light L31 is passedperfectly through the polarized beam splitter 301 with a transmissivityof about 100%.

The quarter wavelength element 302 is provided with the function oftransforming the linearly polarized light into circular polarized light,so that the light L32 for illuminating the object 20 is circularpolarized light. The regular reflection light of the light reflectedfrom the object 20 is the circular polarized light, but transformed intothe linearly polarized light after passed through the quarter wavelengthelement 302. When passed through the quarter wavelength element 302twice, since the linearly polarized light is rotated 90 degrees withrespect to the polarization direction, the regular reflection lightreflected from the object 20 and allowed to be incident upon thepolarized beam splitter 301 becomes a linearly polarized light L33having the vibration component of X-axis direction. The linearlypolarized light is reflected at a right angle by the polarized beamsplitter 301 without being passed therethrough. The diffusion reflectionlight L34 (other than the regular reflection light) of the lightreflected from the object 20 is passed through the polarized beamsplitter 301, passed through the slit 254 of the partial reflectionmirror 251, reflected by the mirror 5, and then image formed on the CCDs7 of the light-electricity transducing elements through the imageforming system 6.

Since the number of the polarizing element 331 is only one, it ispossible to secure a light transmissivity of more than 20%. Therefore,there exists such an advantage that the light utilization efficiency ofthe overall optical system can be improved high. As a result, it ispossible to provide an image reading apparatus high in reading speed, inspite of the illumination unit 1 of a small quantity of light.

FIG. 7 shows a fourth embodiment of the present invention. In thisembodiment, an illumination unit 411, a first polarizing element 421, apartial reflection mirror 451, a second polarizing element 431, and CCDs7 of light-electricity transducing elements are all arranged on the sideof the CCDs 7 relative to the image forming system 6, that is, betweenthe image forming system 6 and the CCDs 7. The first polarizing element421 and the second polarizing element 431 are so arranged that thelinearly polarization directions are perpendicular to each other, inorder to remove the regular reflection light component of the lightreflected from the object 20 and to introduce only the diffusionreflection light onto the CCDs 7.

In the case where the reading width of the object 20 is 22 cm in theprimary scanning direction (corresponding to A4 size), if the image isformed on the CCDs 7 through the image forming system 6 of one-seventh(1/7) reduction ratio, the size of the image is about 3 cm. Since theillumination unit 411 is disposed on the CCD 7 side relative to theimage forming system 6, the light emitting length of the illuminationunit 411 is about 3 cm, thus realizing a small-sized apparatus. Inaddition, the lengths of the partial reflection mirror 451, the firstpolarizing element 421, and the second polarizing element 431 can bereduced to about 3 cm, thus it being possible to reduce the parts cost.

FIG. 8 shows a fifth embodiment of the present invention. In thisembodiment, a high-directivity laser light L51 emitted by a laser lightemitting element 511 is transformed into linearly polarized light, andscanned by a rotating polygonal mirror 512. The scanned light L52 ispassed through a fθ lens 513, reflected at a right angle by a mirror551, passed through a half mirror 541, and then introduced upon areading line S of an object 20 to be image read. The reflected light isreflected by the half mirror 541, passed through a second polarizingelement 531 to remove the regular reflection light, and then imageformed on the CCDs 7 through the image forming system 6.

In this embodiment, since a laser light having an ideal directivity isadopted, it is possible to provide an image reading apparatus high inillumination efficiency and further to reduce the power consumed by theillumination unit markedly.

As described above, in the apparatus according to the present invention,linearly polarized light is irradiated upon an object to be image read;the regular reflection light component of the light reflected from theobject and located on substantially the same plane as the linearlypolarized light is shuttled by the polarizing element arranged in thedirection perpendicular to the polarization plane of the regularreflection light component; and the diffused light component of thereflected light is image formed on the light-electricity transducingelements via the polarizing element.

As described above, according to the present invention, in the imagereading apparatus provided with an illumination unit for illuminating anobject to be image read, and an image forming system for image formingthe light reflected from the object on light-electricity transducingelements, since the major illumination light emitted from theillumination unit and the light reflected from the object and introducedonto the light-electricity transducing elements are both located on thesame plane, it is possible to provide an image reading apparatus high inthe illumination efficiency, which can illuminate the image readingposition effectively.

Further, since the illumination efficiency of the illumination unit ishigh, the light output of the illumination unit can be reduced andthereby it is possible to provide a compact image reading apparatus ofhigh image reading speed.

I claim:
 1. An image reading apparatus comprising:light illuminatingmeans for illuminating an object to be image read substantiallyperpendicularly to the object with linearly polarized light having anillumination width determined by a width to be image read and obtainingreflected light substantially perpendicularly from the object, thereflected light having a first, regular reflection light component and asecond reflection light component; shutting means for shutting out thefirst, regular reflection light component and passing the secondreflection light component; and light-electricity transducing means fortransducing the passed second reflection light component into electricsignals.
 2. The image reading apparatus of claim 1, wherein said lightilluminating means comprises a light source for generating irregularpolarized light; and a first polarizing element for producing thelinearly polarized light from irregular polarized light.
 3. The imagereading apparatus of claim 1, wherein said shutting means comprises asecond polarizing element for passing the linearly polarized light andhaving a polarization plane perpendicular to a polarization plane of theregular reflection light component.
 4. The image reading apparatus ofclaim 1, wherein said light-electricity transducing means comprises aplurality of light-electricity transducing elements arrangedone-dimensionally;and said image reading apparatus further comprises;animage forming system for image forming the reflection light componentonto a plurality of said light-electricity transducing elements; and adiaphragm for changing a focal depth of said image forming system. 5.The image reading apparatus of claim 1, wherein said shutting meanscomprises;a quarter wavelength element for transforming the linearpolarized light for illuminating the object into a first circularpolarized light, and for transforming the regular reflection lightcomponent reflected from the object, as a second circular polarizedlight, into linearly polarized regular reflection light having apolarization plane perpendicular to that of the linearly polarizedlight; and a polarized beam splitter for passing the linearly polarizedregular reflection light in a direction parallel to a direction in whichthe linear polarized light is given to the object and allowing passingtherethrough a reflection light component reflected from the objectother than the regular reflection light component.